Free Ohm's Law Calculator
Solve for voltage, current, resistance and power from any two known values.
What is the Ohm's Law Calculator?
Solve for voltage, current, resistance and power from any two known values.
Using V = I x R and P = V x I, the calculator finds the two missing values from whichever two you enter. Related forms such as P = V squared / R and P = I squared x R cover the other pairings.
Quick, reliable engineering arithmetic saves time on site and in the workshop. These tools show their working so you can check the result.
How to use the Ohm's Law Calculator
Using the ohm's law calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Step 1
Enter your values, choosing the units you are working in.
Step 2
Read the result and the supporting numbers shown beneath it.
Step 3
Check the result against a second method or a reference table before you rely on it.
Tips for better results
Leave unknowns at 0 and enter exactly two values, as extra values are ignored. For mains wiring, follow local electrical codes and use a licensed electrician rather than relying on a hobby calculation.
Keep units consistent from start to finish.
These tools are for estimates. Safety critical designs need a qualified engineer.
Privacy and where your data goes
Everything you type into the ohm's law calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
How many values do I need to enter?
Two. Enter any two of voltage, current, resistance and power, and leave the others at 0.
Which values are used if I enter three?
The calculator picks a pair in a fixed order and ignores the rest, and the 'Calculated from' row tells you which pair was used.
Is the ohm's law calculator free?
Yes. It is free to use with no signup, no watermark and no usage limits.
Is my data private?
Yes. Your inputs are processed in your browser and saved only in its local storage. They are not uploaded to our servers.
Does it work on mobile?
Yes. Zapxa works on phones, tablets and desktops. Use the print button or download a PDF to keep a copy.
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